Isolation and identification of residual chromophores in cellulosic materials

Abstract

A general procedure was developed for the isolation of residual chromophores in or on cellulosic material, which were hitherto inaccessible to structure elucidation due to their extremely low content in the ppb concentration scale. It is applicable to cellulosic pulp, cellulosic fibers (viscose, Lyocell) and cellulose derivatives (acetate, carbonyl-labeled cellulose) as well. The chromophore identification comprises treatment of the cellulosic material with boron trifluoride–acetic acid complex (BF 3·2HOAc) containing sulfite, chromatographic separation of the resulting chromophore-containing mixture, and structure determination of the main constituents by NMR/MS and comparison to authentic samples. Both adsorbed and covalently bound aromatic and quinoid compounds are selectively released by the treatment. Covalent ester, ether and secondary alkyl links between chromophore and cellulose are broken. Four cellulosic example substrates have been analyzed for their chromophore content: Lyocell fibers, cellulose triacetate, pulp after thermal treatment in N, N-dimethylacetamide, and pulp containing carbonyl-selective labels, and up to 11 chromophores per sample have been identified.